Tissue or organ failure due to illness or injury is a major health problem worldwide with little option for full recovery other than organ or tissue transplantation. However, problems finding a suitable donor mean that this option is not available to the majority of patients. tissue engineering or remodeling whereby synthetic or semi synthetic tissue or organ mimics that are either fully functional or which are grown in a desired functionality is currently being investigated as replacements.
One area in particular that this technology is becoming increasingly important is in the cornea of the eye. Corneal transplantation is the most common form of solid organ transplant performed worldwide. Each year around 80,000 are performed in the USA and the UK alone. The prevalence of refractive surgery for correction of myopia such as photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) has led to shortage of suitable cornea for transplant for tissue reconstruction after surgery or disease processes and for tissue manipulation in vivo to engineer changes. In addition, approximately 5% of patients undergoing laser surgery experience unexpected outcomes.
The cornea is a transparent tissue that comprises the central one sixth of the outer tunic of the eye. Its unified structure and function provide the eye with a clear refractive interface, tensile strength, and protection from external factors. The cornea is built from three different main layers of cells: the epithelium, the stroma, and the endothelium (Pepose, J. S. et al., “The cornea; Adler's Physiology of the eye: Clinical application”, 9th ed. St. Louis: Mosby Year Book, 1992, 29-47; Spencer, W. H., “The cornea; Ophthalmic Pathology: an atlas and textbook”, 4th ed., Philadelphia: W. B. Saunders Co., 1996, 157-65). In addition, the Descemet's membrane, the Bowman's layer, and the basement membrane are structures that are derived in some ways from one of these main cellular layers.
The corneal epithelium is the layer in direct contact with the external environment. It is a stratified squamous, non-keratinized structure with a thickness ranging from 40 to 100 μm, in rats and in humans, respectively. It is comprised of a superficial zone, usually formed by two to three layers of flat squamous cells; a middle zone, formed by two or three layers of polyhedral wing cells; and a basal zone consisting of a single row of columnar cells. The stratified corneal epithelium is characterized as a “tight” ion transporting functional syncitium which serves both as a protective barrier to the ocular surface, as well as an adjunct fluid secreting layer assisting the corneal endothelium in the regulation of stromal hydration, and thereby contributing to the maintenance of corneal transparency. The unique and specialized qualities offered by the corneal epithelium have been proven to be essential for the operation of the cornea as the principal refractive element of the eye. It is therefore important that its stratified structure be maintained irrespective of any environmental stresses.
Trauma to the surface of the cornea is highly prevalent; for example, minor scrapes, eye infections and diseases, chemical or mechanical accidents and surgical practice can all damage the cornea. One major complication in post corneal-trauma wound healing is the loss of visual acuity due to tissue reorganization. Patients at risk for ophthalmic healing problems include those who have undergone surgery. Examples of such surgery include, but are not limited to, cataract extraction, with or without lens replacement; corneal transplant or other penetrating procedures, such as penetrating keratoplasty (PKP); excimer laser photorefractive keratectomy; glaucoma filtration surgery; radial keratotomy; and other types of surgery to correct refraction or replace a lens.
The cornea provides the external optically smooth surface to transmit light into the eye. Surgery disrupts the forces which anchor the cornea in its normal configuration. In cataract patients, a full-thickness surgical incision is made in the region of the limbus. The cornea contracts when it heals, causing a local distortion of the tissue and a concomitant distortion in the visual field in the affected region (astigmatism).
Other surgical wounds in the cornea can initiate a wound healing process that causes a predetermined local shift in the curvature of the cornea. The most widely known of these techniques is radial keratotomy (RK), in which several partial-thickness incisions are produced to cause central corneal flattening. This technique, however, is limited due to a lack of predictable results and significant fluctuations in vision, both of which are related to the nature and extent of wound healing (Jester et al., Cornea (1992) 11: 191). For example, a reduction in peripheral bulging of the corneal tissue with an associated regression in the initial visual improvement has been observed in most RK patients (McDonnell and Schanzlin, Arch. Ophthalmol. (1988), 106: 212).
Wounds in the cornea also heal slowly, and incomplete healing tends to be associated with instability of visual acuity (with fluctuations in vision from morning to evening, as well as drifting visual acuity occurring over a period of weeks to months). This may be the cause of 34% or more of patients who have had radial keratotomy complaining of fluctuating vision one year after surgery (Waring et al., Amer. J. Ophthalmol. (1991) 111: 133). Also, if a corneal wound fails to heal completely, a wound “gape” can occur leading to a progressive hyperopic effect. Up to 30% of patients having the RK procedure are afflicted with hyperopic shifts associated with wound gape (Dietz et al., Ophthalmology (1986) 93: 1284).
Corneal regeneration after trauma is complex and not well understood. It involves the regeneration of three tissues: the epithelium, the stroma and the endothelium. Three main intercellular signaling pathways are thought to coordinate tissue regeneration: one mediated by growth factors (Baldwin, H. C. and Marshall, J., Acta Ophthalmol. Scand., (2002) 80: 238-47), cytokines (Ahmadi, A. J. and Jakobiec, F. A., Int. Ophthalmol. Clinics, (2002) 42(3): 13-22) and chemokines (Kurpakus-Wheater, M, et al., Biotech. Histochem, (1999) 74: 146-59); another mediated by cell-matrix interactions (Tanaka, T., et al., Jpn. J. Ophthalmol., (1999) 43: 348-54); and another mediated by the gap junctions and the connexin family of channel forming proteins.
Gap junctions are cell membrane structures, which facilitate direct cell-cell communication. A gap junction channel is formed of two connexins, each composed of six connexin subunits. Each hexameric connexin docks with a connexin in the opposing membrane to form a single gap junction. Gap junction channels can be found throughout the body. A tissue such as the corneal epithelium, for example, has six to eight cell layers, yet expresses different gap junction channels in different layers with connexin-43 in the basal layer and connexin-26 from the basal to middle wing cell layers. In general, connexins are a family of proteins, commonly named according to their molecular weight or classified on a phylogenetic basis into alpha, beta, and gamma subclasses. To date, 20 human and 19 murine isoforms have been identified (Willecke, K. et al., Biol. Chem., (2002) 383, 725-37) perhaps indicating that each different connexin protein may be functionally specialized. Different tissues and cell types have characteristic patterns of connexin protein expression and tissues such as cornea have been shown to alter connexin protein expression pattern following injury or transplantation (Qui, C. et al., (2003) Current Biology, 13: 1967-1703; Brander et al., (2004), J Invest Dermatol. 122(5): 1310-20).
The corneal regeneration process post-trauma can result in the loss of corneal clarity and therefore influence the outcome of refractive surgery. Present treatments for damaged cornea generally include corneal transplant or attempts to use corneal cells/tissue for reconstruction. However, post-operative trauma to the corneal and the surrounding soft tissue following surgical procedures such as, for example, excimer laser photorefractive keratectomy, often results in scarring due to hypercellularity associated with modification of the extracellular matrix; including changes in epithelial cell patterning, myofibroblast differentiation, stromal remodeling, and epithelial hyperplasia at the site of a laser induced lesion.
In severe spinal cord injuries, the pathological changes that occur, whether by transection, contusion or compression, share some similarities with post-operative scar formation and tissue remodeling. Within 24-48 hours after injury, the damage spreads and significantly increases the size of the affected area. A gap junction-mediated bystander effect (Lin, J. H. et al., 1998, Nature Neurosci. 1: 431-432), by which gap junction channels spread neurotoxins and calcium waves from the damage site to otherwise healthy tissue may be involved. This is accompanied by the characteristic inflammatory swelling. The region of damage in the spinal cord is replaced by a cavity or connective tissue scar, both of which impede axonal regeneration (McDonald, J. W. et al, (September 1999) Scientific American. 55-63; Ramer, M. S. et al., Spinal Cord. (2000) 38: 449-472; Schmidt, C. E. and Baier Leach, J.; (2003) Ann. Rev. Biomed. Eng. 5: 293-347). Although progress has been made with some current therapeutic modalities, major constraints to spinal cord repair still remains, including the invasive intervention itself can further lesion spread and glial scar formation, impeding the repair process and risk further loss of neural function (Raisman, G. J. Royal Soc. Med. 96: 259-261).
Antisense technology has been used for the modulation of the expression for genes implicated in viral, fungal and metabolic diseases. U.S. Pat. No. 5,166,195, proposes oligonucleotide inhibitors of HIV. U.S. Pat. No. 5,004,810 proposes oligomers for hybridizing to herpes simplex virus Vmw65 mRNA and inhibiting replication. See also WO00/44409 to Becker et al., filed Jan. 27, 2000, and entitled “Formulations Comprising Antisense Nucleotides to Connexins”, the contents of which are hereby incorporated by reference in their entirety, describes the use of antisense (AS) oligodeoxynucleotides to downregulate connexin expression to treat local neuronal damage in the brain, spinal cord or optic nerve, in the promotion of wound healing and reducing scar formation of skin tissue following surgery or burns. However, many difficulties remain that need to be overcome. It is often the case, for example, that the down regulation of a particular gene product in a non-target cell type can be deleterious. Additional problems that need to be overcome include the short half life of such ODN's (unmodified phosphodiester oligomers) typically have an intracellular half life of only 20 minutes owing to intracellular nuclease degradation (Wagner 1994, supra) and their delivery consistently and reliably to target tissues.
Therefore, there is a need and there are enormous potential advantages for the development of compounds for the problems described above. Such compounds, related compositions, and methods for their use are described and claimed herein.